1. Technical Field
The invention relates to a method for manufacturing integrated circuits; in particular a method for generating corrected patterns for a phase-shifting mask and its associated trimming mask.
2. Discussion of Related Art
In a method generally called an optimal proximity correction (OPC), an initial layout is predetermined for producing a circuit configuration with the aid of a photolithography method. From the initial layout, a pattern is generated for a phase-shifting mask, with the aid of which part of the circuit configuration is to be produced. From the initial layout, a pattern for a trimming mask is also generated, with the aid of which configurations of the circuit configuration adjoining the circuit configuration of the first part can be produced and with the aid of which places are exposed at which there are direct phase transitions of the phase mask. The pattern for the phase-shifting mask and the pattern for the trimming mask are corrected, taking into consideration neighborhoods of the configurations of the patterns having influence on the imaging during the photolithography, in such a manner that a circuit configuration which can be produced by means of the corrected patterns is more similar with regard to the geometry of the initial layout than a circuit configuration which can be produced by means of the uncorrected patterns.
Thus, neighborhood-induced diffraction effects are corrected. During the correction, neighborhoods are taken into consideration which have an influence on the imaging during the photolithography.
The phase-shifting mask is either a dark-field mask or a bright-field mask. For example, a phase-shifting mask of the dark-field type contains at least two types of radiation-transparent regions with mutually different influence on the phase of electromagnetic waves transmitted through the permeation regions. Usually, a phase shift of 180xc2x0 is generated between adjacent permeation regions.
A method with the above-mentioned method steps is explained in the article xe2x80x9cIntegration of Optical Proximity Correction Strategies in Strong Phase Shifters Design for Poly-Gate Layersxe2x80x9d by Christopher Spence, Marina Plat, Emile Sahouria, et al. This article is a part of the 19th Annual BACUS Symposium on Photomask Technology, Monterey, Calif., September 1999 and published in SPIE, Vol. 3873, pages 277 to 287. During the correction, the patterns for the phase-shifting mask and the trimming mask are corrected simultaneously. In the publication, circuit configurations having a critical dimension CD of 100 nm are produced with the aid of 248 nm lithography devices. In addition, the production process is simulated. However, configurations shown in the publication have comparatively large distances from one another. The ratio between minimum spacing of the configurations and minimum configuration width is much greater than two.
It is the object of the invention to specify an improved OPC method for correcting patterns for a phase-shifting mask and its trimming mask. In addition, an associated device, an associated program, a data medium with this program and an integrated circuit configuration are to be specified.
The object relating to the method is achieved by the method steps specified in patent claim 1. Further developments are specified in the subclaims.
The invention is based on the consideration that phase-shifting masks are usually used for producing circuit configurations, the critical dimension of which is so small that during the imaging of the configurations with the aid of the masks, neighborhoods of the configurations influence the imaging. Although simultaneous correction of the pattern of the phase-shifting mask and of the pattern of the trimming mask is possible, it is associated with a comparatively great expenditure because the influence of the neighborhoods on the imaging during the photolithography can be estimated only with difficulty.
In the method according to the invention, the pattern for the phase-shifting mask is firstly corrected in accordance with correction rules for the pattern of the phase-shifting mask in a first correcting step in addition to the method steps initially mentioned. Subsequently, the pattern for the trimming mask is corrected in accordance with correction rules for the pattern of the trimming mask with use of the corrected pattern for the phase-shifting mask in a second correction step. Separating the correction of the pattern for the phase-shifting mask from the correction of the pattern for the trimming mask has the result that, during the correction method, not so many different influences need to be taken into consideration at the same time. The influence of the neighborhoods on the imaging during the photolithography can thus be controlled more easily. Overall, the expenditure for the correction is much less in the method according to the invention than with simultaneous correction of both patterns.
In an alternative of the method according to the invention, the pattern for the trimming mask is firstly corrected in accordance with correction rules for the pattern of the trimming mask in a first correction step. Subsequently, the pattern for the phase-shifting mask is corrected in accordance with correction rules for the pattern of the phase-shifting mask with use of the corrected pattern for the trimming mask in a second correction step. The order of correction steps can thus be selected. The order is established in such a manner that the simplest possible correction rules can be set up.
In a further embodiment, the pattern for the phase-shifting mask is corrected with use of the uncorrected pattern for the trimming mask in the first correction step. As an alternative, the pattern for the trimming mask is corrected with use of the uncorrected pattern for the phase-shifting mask in the first correction step. These measures make it possible to determine more accurate correction rules.
In the first correction step, essentially all corrections or, respectively, all corrections which can be performed for the first corrected mask on its pattern in accordance with the predetermined correction rules are preferably performed. In the second correction step, essentially all or, respectively, all corrections which can be performed on the pattern of the mask corrected as the second mask in accordance with the correction rules predetermined for the second mask to be corrected at the time of the performance of the method are then performed. Essentially all this means is that, for example, individual corrections can still be performed later manually in the sense of a touch-up. Thus, corrections are performed at all places of the pattern at which corrections can be performed in accordance with the correction rules. Thus, the correction steps are clearly separate from one another.
For example, the following is done on the basis of the correction rules:
Line shortenings during the production of the circuit configuration in comparison with the pattern or, respectively, initial layout are eliminated by lengthening of the relevant configuration in one of the two patterns,
Roundings of corners in the circuit configuration produced or, respectively, Roundings of corners occurring during the simulation of the production are avoided by xe2x80x9cadding piecesxe2x80x9d of correction areas in one of the two patterns, and
Narrowings in the circuit configuration produced or, respectively, simulated are avoided in that the configurations causing these circuit configurations are widened in the areas of the narrowing in one of the two patterns.
In a further embodiment of the invention, the correction is essentially ended after the second correction step has been performed, i.e., for example, apart from slight manual touch-ups.
The patterns generated with the aid of the method according to the invention or, respectively, with the aid of its further developments are used as the basis in the production or the simulation of the production of a phase-shifting mask and of a trimming mask. For example, mask data are generated which can be entered directly into a mask writer. If, in contrast, the production process is simulated, masks can be developed for circuit configurations which will only be produced in one or two years because the devices needed for the production are still being developed. Due to the simulation of the production of the circuit, faults in the pattern can be detected and corrected at a very early stage. In this case, the method according to the invention or, respectively, its further developments are performed a number of times, using instead of the initial layout a new initial layout. As an alternative or additionally, changes can also be made in the original pattern for the phase-shifting mask and/or in the pattern for the trimming mask.
In a next further development, the patterns are defined by mask data. The method is performed with the aid of at least one data processing system. In an embodiment, the correction is performed automatically. The further development and the embodiment are used, in particular, for preparing the production of very-large-scale integrated circuit configurations, e.g. of microprocessors or memory chips. Thus, the correction of several million part-configurations of the patterns can be performed in a simple manner and with justifiable expense.
The invention also relates to a device for correcting patterns for a phase-shifting mask and its trimming mask, especially a data processing system. The device contains a memory unit for storing the data of the initial layout, the data of the pattern for the phase-shifting mask and the data of the pattern for the trimming mask. A correction unit performs the correction of the pattern of the phase-shifting mask and the correction of the pattern of the trimming mask. During this process, the two above-mentioned correction steps are performed one after the other. The technical effects mentioned above in connection with the method according to the invention thus also apply to the device according to the invention.
In further developments, the device is constructed in such a manner that, in operation, it performs a method according to a further development of the method according to the invention. For example, the correction is performed automatically.
The invention also relates to a program for correcting patterns for a phase-shifting mask and its trimming mask. On the execution of the instructions of the program by a processor, the correction steps of the method according to the invention are performed. The above-mentioned technical effects thus also apply to the program.
In a further development, some of the instructions of the program are contained in a file which contains instructions of a command language for controlling the program sequence. By using so-called script files, programs which, in principle, are suitable for performing the method but in which the contents of the script file have not yet been transferred into the source code can be used for performing the method according to the invention. This transfer can be done at a later time. A program which is suitable for performing the method with the aid of a script file is, for example, the program xe2x80x9cOptissimoxe2x80x9d by aiss GmbH, Munich, Germany, in the year 2000 version.
In a next further development of the program according to the invention, the program is configured in such a manner that during the execution of its instructions, a method according to one of the above-mentioned further developments of the invention is performed. Accordingly, the above-mentioned technical effects also apply to the further developments of the program.
The invention or, respectively, its further developments allow integrated circuit configurations to be produced, for the minimum critical dimension of which the following holds true:
MinCD=k1*xcex/NA, 
where xcex is the wavelength of a radiation source used during the production for exposing a radiation resist, NA is the numeric aperture of projection optics used during the production and k1 is an empirical factor. Currently, radiation sources having a wavelength of 248 nm are usually used. However, the use of radiation sources with 193 nm or, respectively, 157 nm is already foreseeable. The numeric aperture is, for example, between 0.6 to 0.85. Moreover, the ratio between the minimum spacing of the configurations and the minimum configuration width is less than 1.5, i.e. the configurations are comparatively dense. The empirical factor k1 is less than 0.35 or corresponds to this value.
The invention also affects circuit configurations which are produced by using masks, the patterns of which are predetermined in accordance with the method according to the invention. Furthermore, a phase-shifting mask and a trimming mask are protected which have been produced with the aid of the method according to the invention or one of its further developments.